The invention relates to a guide pin assembly for aligning the upper hold down plate of the top nozzle of a fuel assembly with the upper core plate of a pressurized water nuclear reactor.
Fuel assemblies for pressurized water nuclear reactors are supported within the reactor core by upper and lower core plates. The upper and lower core plates are supported by a core support barrel, which in turn surrounds the reactor core and extends between the ends thereof. The number of fuel assemblies within the reactor core varies according to the size of the reactor core.
Such fuel assemblies include a plurality of guide tubes through which the control rods are inserted and withdrawn from the reactor core. The guide tubes are supported between a top nozzle and a bottom nozzle. The top nozzle includes an upper hold down plate, a lower adapter plate, and an enclosure forming a sidewall and extending between the upper hold down plate and the lower adapter plate. Generally, the top nozzle has a square cross-section, and includes a plurality of guide tubes, the number of which varies according to the size of the fuel assembly. The upper hold down plates of a plurality of top nozzles are aligned with, and secured to, the upper core plate to support a plurality of fuel assemblies below the upper core plate. The upper core plate and upper hold down plates of the top nozzles include aligned bores therethrough for the guide tubes.
As further described in U.S. Pat. No. 4,534,933 to Gjertsen et al., and assigned to the assignee of the present invention, guide pins are disposed between the upper hold down plate of the top nozzle of each fuel assembly and the upper core plate to properly align the upper core plate and the upper hold down plate of the top nozzle of the fuel assembly so that the guide tubes extend vertically. U.S. Pat. No. 4,534,933 is incorporated herein by reference. These guide pins must sometimes be replaced. The replacement of missing, broken or damaged guide pins is difficult without risking the exposure of plant personnel to dangerous levels of radiation.
It is an object of the invention to develop a remotely installable guide pin assembly for aligning the upper core plate of the reactor with the upper hold down plate of the top nozzle of a fuel assembly.